Acid treatment of anthraquinonethiazole vat dyestuffs



Patented Nov. 9, 1948 umreo STATE ear insane ENT oEFics ACID TREATMENT OFANTHEAQUINONE- .TH-IAZOLE VAT DYESTUFFS John F. Cullinan and Lawrence-D. Lytle, Plain'- field, N. .l., assignors toAmerican Cyanamid Company, New York Maine i N. Y., a corporation: of

No Drawing... Application March 13, 19.44;

l Serial N0. 526,343

5' Claims.

l This" invention relates to an improved process oftransforming'vat colors into a form having avery*fine and substantially uniform particle size;

More particularly'th'e present invention relates.

to animproved process whereby dyestuffs in the desired uniform, finelyivided state are obtained from vat dyestuffs of the type characterized by i the inclusion of one or more anthraquinonenuclei andone or' more thiazole nuclei. Typical representative dyestufis of this type include'1,2,5,6- anthraquinone-C-diphenyl dithiazole of the following formula: i

and 3,4,3A'-benzidine-C-di-beta-anthraquinonyl dithiazole having the following structural formula:

' As is well known, vat colors are normally obtained as coarse crystalline materials or as relatively large agglomerated particles. In this state,

. they are unsuitable for use imprinting, pigment drowning the entire solution in a large excess of water. Modifications have. been proposed in which the dilution is carried out in other ways.

These have included, for example, addition of dilute sulfuric acid in a quantity only suflicient 'toprecipitate a sulfate which canbe collected and. hydrolysed; or accomplishing the dilution I with water of crystallization by using such by 'drated materials as Glaubers salt and the like.

The. effect of varying the operating temperatures hasalso been proposed as ameans of control.

While-the art has succeeded in obtaining finer particle sizes, the importance of. uniformity, and

. a 2 its necessary relation to 1y considered. In general, therefore, vat colors as prepared according to the teachingsof the prior art generally lacked sufiicient uniformity of ent invention to develop such a process, capable particle size and contained larger particles in addition to the small ones. As a result, there re. mained a demand'for a methodadapted to produces, more finely divided color of more uniform size.

It is, therefore, a principal object of. the .presof producing particles having the desirable properties of fineness and uniformity of particle: size.

In general, the desired object is accomplished through an improved process of carrying out the treatment of the materials with sulfuric acid.

According to the "present invention, it has been found that in the treatment with sulfuric acid, there is for each material a specific range of acid concentrations which produce the optimum result. In addition, it hasbeen foundthat the proportions between the dissolved and undissolvedmaterialat any stage in the process is of equal, if not greater importance.

This involves notonly the acid concentration, but also the total amount of acid present. Variations also result from changing the temperature at which the reaction is carried out, the procedure by which the correct acid concentration is reached and. to a lesser extent with the time of contact. All must be reasonably controlled for thebest results.

In developing the present process, the optimum acid concentration and amounts aresuch that 60.; far;:apart and .their...rate.. of; aggregation in preisrconverted to its sulfate. is less soluble; the; solution becomes supersatu- 5a onlya very small quantity of dyestuff is dissolved and the dye is precipitated as its sulfate. It is necessarythat the dyestuff have some solubility, otherwise it cannot be converted into a sulfate, and it' is further necessary that at least one of its sulfates be slightly less soluble; It is the recognition and useof this differential solubility between the dyestuif and its sulfate which is-re' sponsible for'the surprisingly improved results obtained by the process. slightly soluble,.goes into a solution as such and But because the salt rated with respect to the sulfate and the latter separates out. l

Itshouldbe noted that at any given time the solution of the sulfate is exceedingly dilute. Consequently, the: dissolved molecules are relatively fineness was not proper- The dyestuff, being cipitating the insoluble sulfates is very low. At the same time, because the concentration of sulfate remains essentially constant during the entire precipitation, the precipitated products, are not only very finely divided but have a very uniform size. Probably due to a pseudomorphosis, this fineness and uniformity is retained when they are subsequently hydrolysed with water, either with or without being previously isolated.

Expressed in general terms, therefore, the process of the present invention comprises the treatment of vat dyestuffs characterized by the presence of one or more anthraquinone nuclei together with one or more thiazole nuclei with the correct amount of sulfuric acid having the optimum concentration. At the same time, the proper degree of care is exercised in bringing the acid to the correct concentration before use and in maintaining a substantially uniform temperature throughout the process.

According to the above considerations, the principal factors to be controlled are: (1) the acid concentration; (2) the amount of acid; (3) the temperature; and (4) the manner of reaching the optimum acid concentration. Each of these has a direct bearing on the treatment of any particular dyestuif. Consequently, each factor is subject to certain limitations.

As far as the acid concentration is concerned, the individual dyestuffs vary widely in their optimum acid ranges. For any particular dyestuff the exact acid range most suitable thereto can not be assigned numerical limitations which will in turn be applicable to all cases. Functionally, a more exact limitation can be assigned in terms of solubility. The lower limit is that acid concentration at which the specific dyestuff has a slight solubility. The upper limit is that concentration at which a sulfate of the dyestufi has only a very limited solubility so as to form readily a supersaturated solution of the sulfate.

In treating anthraquinone-thiazole type dyestuffs according to the process of the present invention, it is important that the sulfuric acid be diluted to the proper concentration before being used. If the dyestufi is dissolved first in concengreat an amount of acid will dissolve excessive trated acid and the resultant solution is then 1 diluted to the proper strength, the desirable result is not obtained. In some cases the dyestuff itself is attacked by the concentrated acid. In other cases only a coarse material is obtained because precipitation by diluting a rather concentrated solution favors the formation of large particles. It is desirable, therefore, to have the initial concentration as low as is practically possible.

So far as the amount of acid used is concerned, at least of the solid products present should remain undissolved at any point in the process. Preferably, the undissolved material should be as great as practically possible so that 98%, or more, remains undissolved. Because the amount of undissolved material present during the process is an important consideration, there is obviously an interrelation between the acid concentration and the amount of acid used. The latter, however, is not as critical as the former. As pointed out above, the amount of acid used may vary. To a certain extent this is limited by practical considerations. Obviously, an insufficient amount of acid produces a very thick, unstirrable slurry. On the other hand, too great an amount of acid is impractical because of the volume required and the consequent decrease in the productive capacity of the equipment.v At the same time, too

amounts of the dyestuff and sulfate. As was indicated above, this is undesirable if the optimum fineness and uniformity of particle size is to be obtained.

For all practical purposes, the amount of acid required will be found to be not less than 10 or more than 40 parts per part of dyestuif. However, in all but extreme cases, these limits can be considerably narrowed. It is usually found that good results will require using between about 20 to 30 parts of acid per part of dyestuif. Because of the relation to the acid concentration, the amount in some cases may require adjustment with respect thereto.

Because in effect, it is the solubilities of the various materials which it is necessary to control, the problem of temperature cannot be overlooked. Marked changes in temperature will alter the solubility of materials in any designated strength of acid. Therefore the temperature of the reaction should not be allowed to vary sufliciently to appreciably affect the solubility during the course of the reaction. It is most convenient to Work at approximately room temperature. Consequently, the experimental data. taken in developing the present invention is based on temperatures of about 2535 C. However, should it become desirable to operate at higher or lower temperatures, an adjustment in either or both the strengthand amount of acid to compensate therefor can be readily made in accordance with the solubility limitations set forth above.

The time cycle should also be considered. Obviously, if the time of contact is too short,

all of the pigment will not be converted into' finely-divided sulfate. On the other hand, if the time of contact is unduly prolonged, particles of precipitated sulfate will graduallyv growbecause. of the known tendency of crystals to in crease in size when maintained in contact with a saturated solution of the mother liquor. There is some inter-relation between the time cycle and the acid concentration. However, in the instant invention, this is relatively unimportant since the range of optimum acid concentrations is so close that the time cycle varies but little between the upper and lower limits.

After conversion to the finely-divided sulfate is complete, the dyestuff must be hydrolysed. This may be done either before or after isolation. A good general practice is to drown the slurry in about 4 to 8 times its volume of water. The precipitated product may then be isolated after diluting the solution to a convenient acid strength for practical filtration. Subsequently, the dyestuff is usually washed on thefilter until neutral. Preferably, but not necessarily, this washed filter cake is subjected to further treat-- ment with a suitable deflocculating agent;

As an indication of the efficiency of the process, the following test has been found particularly useful. A stuff is suspended in 200 ml. of distilled Water at about 50 C. and approximately one-half of this suspension is poured on a three inch conical, glass filter funnel fitted with a dry No. 1 Whatman filter paper. The suspension is allowed to filter by gravity. If the dyestuff is finely divided and uniformly dispersed, most of it should go through the filter into the filtrate and the residue on the paper should be small.

Test dyeings are then carried out, using the filtrate and the unfiltered portion of the suspension, the strengths of the resultant dyeings being compared. The filtrate of a well-dispersed About 100-200 mg. of dispersed dyeproduct gives a dyeing having about 75-90%, the strength of the unfiltered product. It is readily apparent that the greatest dye strength from the filtrate is obtained only when the procedure of the present invention has been carried out so as to produce a maximum of finely divided particles of uniform size.

It is surprising, and entirely unexpected, in view of the prior art teaching that the use of more concentrated acids than are indicated by the limits of the present process produces a great amount of coarser particles as shown by the filtration test. Probably it is due to the fact that the strengths of acids usually prescribed by the prior art have too great a solvent action on the dyestuif. As a result the solute molecules are closer together and have a greater chance to precipitate as larger particles of the sulfate. Obviously also, still more concentrated acid will dissolve substantially the dyestuif, so that the sulfate will be precipitated only after dilution. This is the customary old acid pasting method and subject to all the ordinary faults which have been noted above.

Thus the principal advantage of the present invention lies in its ability to produce very small particles of uniform size. This uniformity of small particle size is of great importance, for example, in a pigment padding process. In such a process, fineness is essential to good penetration but if the particle size is not uniformly small, the coarser particles do not penetrate to the same extent as the finer material and uneven dyeings result. Similarly, in printing vat dyestuffs a fine product size is important in order that reduction may take place quickly but if uniformity is lacking the resultant print is not properly level.

The invention will be more fully illustrated in connection with the following examples in which all parts are by weight unless otherwise noted.

Example 1 One part by weight of the dyestuff of Formula 1 1 given above is treated with parts by weight of the sulfuric acid for 17 hours. When the strength of the acid was 68.7% a rather non-uniform material containing coarse particles was obtained; the filtration test showed that the filtrate had only -40% dyeing strength of the non-filtered product. gave a very uniform, excellently dispersed material. The filtration test gave a filtrate showing in both cases 90% of the dyeing strength of the unfiltered product. When the acid concentration was slightly increased to 74.1% again a much less favorable dispersion was obtained and the filtration test gave a filtrate with only -50% of the dyeing strength of the unfiltered product. During the treatment with acids of the just given strengths, the sulfate was precipitated in the form of yellow crystals. When, however, a sulfuric acid of 98.5% was used the dyestufi went into solution; after drowning in water, a very poorly dispersed dyestuif was obtained. The finely dispersed product obtainable from 70.6% and 72.6% acids requires less caustic soda and less hydrosulfite in its reduction.

Emmple 2 When this dyestuff is first dissolved in concentrated sulfuric acid, diluted to produce a slurry in the same amount of sulfuric acid of the same concentration as used above, and stirred for 17 hours, a very poorly dispersed pigment is obtained. In this case the filtration test showed that the However, acid strengths of 70.6 and 72.6%

6 filtrate had only a 15% dyeing strength of the non-filtered product.

We claim:

L'The method of converting a vat dyestuff, characterized by at least one anthraquinone and at least one thiazole nucleus, into very finely divided particles of substantially, uniform size which comprises forming a slurry of one part of the dyestuff with 20 to 30 parts of sulfuric acid of such concentration that at the operating tem perature at least a part, but not more than ten percent by weight of the total dyestuff is in solution at any one time, agitating this slurry until conversion of the dyestuff to a substantially insoluble sulfate is substantially complete, hydrolyzing the sulfate to the dyestuff and collectin the sotreated dyestufi.

2. A method according to claim 1 in which the concentration of acid used is so balanced that not more than two percent by weight of the dyestuif is in solution at any time during the operation.

3. The method of converting a vat dyestuff comprising 1,2,5,6-anthraquinone-C-diphenyl dithiazole into very finely divided particles of substantially uniform size which comprises forming a slurry of one part of the dyestuff with 20-30 parts of sulfuric acid at about 25-35 C., the acid being used in such concentration that at least a part but not more than ten percent by weight of the total dyestuff is in solution at any one time, agitating the slurry at about 25-35 C. until conversion of the dyestuff to substantially insoluble sulfate is substantially complete, hydrolyzingthe sulfate to the dyestuff and collecting the sotreated dyestuff.

4. A method according to claim 3 in which the concentration of acid used is such that not more than 2% of the total dyestuff is dissolved at any one time during the operation.

5. The method of converting a vat dyestuff comprising 1,2,5,6-anthraquinone-Cdiphenyl dithiazole into very finely divided particles of substantially uniform size which comprises forming a slurry of one part of the dyestuff with 20-30 parts of from about 70.6% to about 72.6% sulfuric acid at about 25-35 C., agitating the slurry at this temperature until conversion of the dyestuff to a substantially insoluble sulfate is substantially complete, hydrolyzing the sulfate to the dyestuff and collecting the so-treated dyestuff.

JOHN F. CULLINAN. LAWRENCE D. LYTLE.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,090,621 Isler Mar. 17, 1914 1,126,475 Isler Jan. 26, 1915 1,145,934 Steindorf et a1 July 13, 1915 1,459,536 Kacer June 19, 1923 1,891,448 Rintelman Dec. 20, 1932 2,026,623 Fleysher Jan. 7, 1936 2,028,104 Graham Jan. 14, 1936 2,065,928 Waldron Dec. 29, 1936 2,090,511 C'rossley Aug. 17, 1937 2,131,419 Herrett Sept. 27, 1938 2,132,190 Rosch Oct. 4, 1938 2,179,551 Graham Nov. 14, 1939 2,204,970 Rintelman June 18, 1940 2,225,302 Hartwell Dec. 17, 1940 2,278,973 Carr Apr. 7, 1942 2,335,698 Rintelman Nov. 30, 1943 

